Editor code: tidy up BOOLs,NULLs and overrides pt1.

A few 'typedefs' replaced by 'using's
This shouldn't have any functional changes at all, just c++17 modernization
It's a part 1 of a split #2847

Signed-off-by: Nemerle <nemerle5+git@gmail.com>

Code/Editor/Core/QtEditorApplication.cpp

@@ -423,7 +423,7 @@ namespace Editor
             {
                 UINT rawInputSize;
                 const UINT rawInputHeaderSize = sizeof(RAWINPUTHEADER);
-                GetRawInputData((HRAWINPUT)msg->lParam, RID_INPUT, NULL, &rawInputSize, rawInputHeaderSize);
+                GetRawInputData((HRAWINPUT)msg->lParam, RID_INPUT, nullptr, &rawInputSize, rawInputHeaderSize);
 
                 AZStd::array<BYTE, sizeof(RAWINPUT)> rawInputBytesArray;
                 LPBYTE rawInputBytes = rawInputBytesArray.data();